Process for producing a kaolin clay product

Abstract

A process for producing a high brightness, high solids kaolin clay aqueous slurry. An aqueous low solids suspension of crude kaolin clay is degritted, and subjected to a particle size classification. The aqueous suspension of the fine particle fraction is acidified to a pH of 5.0 or lower to produce an acid flocculated suspension which is treated with a bleaching agent to reduce ferric ion impurities to ferrous ion impurities. A ferrous ion chelating agent is added to the bleached acid flocculated suspension after which an alkaline agent is added to raise the pH to a level greater than 5.0 to form a dispersed aqueous suspension of the beneficiated kaolin. The dispersed suspension is then subjected to membrane filtration to partially dewater same, and additional water is thermally evaporated from the partially dewatered dispersed kaolin suspension to produce the high solids product suspension.

What is claimed is: 
     
       1. A process for producing a high brightness kaolin clay product of beneficiated kaolin clay particles in a high solids aqueous slurry, comprising: a. forming an aqueous suspension of crude kaolin clay at a relatively low solids content of less than about 70% by weight of kaolin particles;   b. degritting the aqueous suspension of crude kaolin clay to remove kaolin clay particles having a particle size greater than about 325 mesh to form a degritted aqueous suspension;   c. fractionating the degritted aqueous suspension of crude kaolin clay to produce a finer fraction having a particle size distribution wherein at least about 80% by weight of the particles have a particle size less than 2 micrometers equivalent spherical diameter;   d. acidifying the aqueous suspension of relatively fine-particle size kaolin clay particles to a pH at least less than 5.0 to produce an acid flocculated suspension;   e. contacting the acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles with a bleaching agent to reduce ferric ion impurities contained therein to ferrous ion impurities;   f. adding a ferrous ion chelating agent to the bleached acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles whereby the ferrous ions are chelated;   g. admixing an alkaline agent with the bleached acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles to raise the pH to a level greater than 5.0 to form a dispersed aqueous suspension of beneficiated kaolin clay particles;   h. subjecting the dispersed aqueous suspension of beneficiated kaolin clay particles to membrane filtration to partially dewater the dispersed aqueous suspension of beneficiated kaolin clay particles; and   i. thermally evaporating additional water from the partially dewatered dispersed aqueous suspension of beneficiated kaolin clay particles to produce a high solids product suspension of beneficiated kaolin clay particles.   
     
     
       2. A process as recited in claim 1 wherein the aqueous suspension of relatively fine-particle size kaolin clay particles is acidified to a pH of 3.0. 
     
     
       3. A process as recited in claim 1 wherein the aqueous suspension of relatively fine-particle size kaolin clay particles is acidified to a pH at least less than about 3.0. 
     
     
       4. A process as recited in claim 1 wherein the aqueous suspension of relatively fine-particle size kaolin clay particles is acidified by adding sulfuric acid thereto. 
     
     
       5. A process as recited in claim 1 wherein the step of adding a ferrous ion chelating agent to the bleached acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles whereby the ferrous ions are chelated comprises admixing citric acid into the bleached acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles at treatment level ranging from 0.1 to 10 pounds of citric acid per ton of dry clay. 
     
     
       6. A process as recited in claim 3 wherein the pH of the bleached acid-flocculated aqueous suspension of relatively fine-particle size kaolin clay particles is raised to a level between about 6.0 and about 7.0. 
     
     
       7. A process as recited in claim 1 wherein the dispersed aqueous suspension of beneficiated kaolin clay particles is preheated prior to membrane filtration. 
     
     
       8. A process as recited in claim 1 wherein the degritted aqueous suspension is fractionated to a particle size distribution wherein from about 90% to about 95% by weight of the particles have a particle size less than 2 micrometers equivalent spherical diameter. 
     
     
       9. A process for beneficiating a crude kaolin to produce a high brightness kaolin clay product of beneficiated kaolin clay particles in an aqueous slurry, comprising: (a) forming an aqueous suspension of said crude kaolin clay and degritting and fractionating the aqueous suspension to produce an aqueous suspension of fine-particle size kaolin clay particles;   (b) acid flocculating said fine particle size suspension at a pH of 5.0 or lower and bleaching said slurry under said acid conditions to reduce ferric ion impurities contained therein to ferrous ion impurities;   (c) adding a ferrous ion chelating agent to the bleached acid flocculated aqueous suspension of relatively fine-particle size kaolin clay particles whereby the ferrous ions are chelated;   (d) raising the pH of the bleached acid flocculated aqueous suspension of fine-particle size kaolin clay particles to a level greater than 5.0 to form a dispersed aqueous suspension of beneficiated kaolin clay particles; and   (e) subjecting the dispersed aqueous suspension of beneficiated kaolin clay particles to membrane filtration to at least partially dewater the said suspension.   
     
     
       10. A process as recited in claim 9, wherein step (b) is conducted at a pH of about 3.0. 
     
     
       11. A process as recited in claim 9, wherein step (b) is conducted at a pH lower than about 3.0. 
     
     
       12. A process as recited in claim 9, wherein the aqueous suspension of relatively fine-particle size kaolin clay particles is acidified by adding sulfuric acid thereto. 
     
     
       13. A process as recited in claim 9, wherein the step of adding a ferrous ion chelating agent to the bleached acid flocculated aqueous suspension of fine-particle size kaolin clay particles whereby the ferrous ions are chelated, comprises admixing citric acid into the bleached acid flocculated aqueous suspension at treatment level ranging from 0.1 to 10 pounds of citric acid per ton of dry clay. 
     
     
       14. A process as recited in claim 11, wherein the pH of the bleached acid-flocculated aqueous suspension of fine-particle size kaolin clay particles is raised in step (d) to a level between about 6.0 and about 7.0. 
     
     
       15. A process as recited in claim 9, wherein the dispersed aqueous suspension of beneficiated kaolin clay particles is preheated prior to membrane filtration. 
     
     
       16. A process as recited in claim 9, wherein the degritted aqueous suspension is fractionated to a particle size distribution wherein from about 90% to about 95% by weight of the particles have a particle size less than 2 micrometers equivalent spherical diameter.